The present invention relates to a drive shield for use in tunnel driving and to a method of operating such a shield.
In the driving of tunnels, adits, trenches or the like it is known in the art to use a drive shield composed of elongate drive members or cutter planks arranged side-by-side and supported on a frame structure. Fluid rams are connected between the frame and the drive members and the rams are operated to advance the drive members in the driving direction and then to draw up the frame ready for the next cycle. When the frame is shifted up the drive members provide an anchorage or abutment for the shifting forces. When the conditions allow slippage between the surrounding wall and the members there can be problems when the frame is shifted and ideally all the members should remain in tight frictional contact with the wall when the frame is shifted. There is, however, inevitably a significant difference between the frictional resistance encountered by the drive members in the upper region of the shield and the frictional resistance encountered by the drive members in the lower region of the shield since the latter members usually carry the weight of the excavating machine or other equipment employed to remove the spoil. This is especially the case where tunnels are excavated at shallow depths. In view of this, certain individual drive members or groups of members can become displaced when the frame is shifted up and this creates serious problems.
To overcome this problem it is known to provide anchoring devices on some of the members. These anchoring devices then grip the wall to prevent the slippage of the member in question. These measures are somewhat costly since the devices need to be selectively operated to release or grip the wall and moreover these measures are not fully effective in overcoming the problems discussed.
A general object of this invention is to provide an improved drive shield and method of operating the same.